Fluidic sprinkler heads have been widely applied to irrigation in the agricultural area. At present, as the related patent applications, there are Fluidic Sprinkler Head (No. 03222424.9) and Wall-attached Fluidic Sprinkler Head (No. 200710134562.5). A fluidic sprinkler head generally has two states: direct jet and wall attachment. The switchover between the two states is adjusted by discontinuously intercepting signal water in a signal nozzle by a fluidic sprinkler head. The applicant(s) once submitted one patent, titled “External Water Jet Wall-attached Control Element” (No. 201010552792.5), where the control element includes a reverse air supply pore, an external water signal nozzle, an outlet cover plate, a conduit and a water inlet. The signal water or air taken from the external water signal nozzle intermittently forms a low pressure vortex area on one side of a main jet, and the reserve air supply pore is opened or closed to allow switchover between high pressure and low pressure on the other side of the main jet. Consequently, a pressure difference is formed between left and right sides of the main jet, and the wall attachment of water flow is thus realized. The wall-attached water flow impacts the chamfer of the outlet cover plate and generates a driving force to drive the sprinkler head to rotate, thereby realizing functions of direct jet, stepping and reverse rotation of the sprinkler head in an automatic control manner. This external water jet wall-attached control element operates stably and reliably, and the outlet cover plate may be designed into any shape.
However, as the signal water intercepted by the existing fluidic sprinkler heads is generally air-water mixture, the duration of direct jet or wall attachment of the fluidic sprinkler head is quite random every time, and there are disadvantages that the stepping frequency is not uniform and the duration of direct jet or wall attachment cannot be controlled accurately; furthermore, the existing fluidic sprinkler heads further have the disadvantage that they may fail to take signal water to complete the rotation action in some exceptional circumstances. This technical problem has become one of the main bottlenecks for the development of fluidic sprinkler heads. Therefore, developing an automatic control element which may ensure uniform stepping frequency of a fluidic sprinkler head is of great importance in promoting the development of irrigation agriculture.